In recent years, display devices employing thin-film transistors as a semiconductor device have been commercialized. Examples of such display devices are liquid crystal displays, organic electroluminescent displays and the like.
A display device of this type comprises an array substrate on which thin-film transistors, interconnecting traces such as signal lines, gate lines and source-drain electrodes, a passivation film and the like are formed. The thin-film transistors and various interconnecting traces are patterned into predetermined forms by such methods as photolithography and dry etching.
In the process of manufacturing a display device, if an array substrate for display device is formed on a large-sized substrate, the in-plane evenness of processing is degraded. For example, in the chamber where the etching is performed, the density of radical species or ionic species easily disperses from the central portion to a peripheral portion of the substrate if it is large because of the influence of exhaust gas or the like (that is, a difference in ratio [density distribution] is easily produced). Therefore, the forms of the interconnecting traces, electrodes and the like are likely to differ from the central portion of the large-sized substrate to the peripheral portion.
Moreover, if the substrate is large, it is hard to attract radicals and ions to the substrate side in the etching step because of its specification, and further re-deposition on the sidewall of a portion to be etched is not sufficient, making it easy to cause progression of side etching. That is, the taper angle of the etching surface tends to be small. Alternatively, the re-deposition tends to be uneven, and further the sidewalls tend to be rough. For these reasons, it is difficult to obtain a processed form as designed in etching.